Slow wave line for electron discharge device



March 1957 TAKEO HUKUNAGA SLOW WAVE LINE FOR ELECTRON DISCHARGE DEVICE Filed June 29, 1965 INVENTOR K50 z/Ku/VA A United States Patent 3,309,630 SLOW WAVE LINE FOR ELECTRON DISCHARGE DEVICE Taken Hukunaga, a Ouemachi, Kumamotoshi, Japan Filed June 29, 1965, Ser. No. 467,847 Claims prierity, application Japan, July 3, 1964,

7 Claims. (Cl. 333-31) This invention relates to electron discharge devices which operate in the microwave region, and more particularly to improvements in the disk loaded waveguide slow wave structure of such devices.

The principal objects of this invention are to provide a slow wave structure having a wide band-pass and a high impedance compared with conventional slow wave structures.

All of the objects, features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, in which:

FIGS. 1a-1d show schematically an example of a disk loaded waveguide slow wave structure of a conventional electron discharge device,

FIGS. 2a-2d show schematically one embodiment of the slow wave structure constructed in accordance with the principles of this invention, and

FIG. 3 shows schematically another embodiment of the slow wave structure according to this invention, wherein two coupling slots are connected with a thin slit.

In FIGS. 1 and 2, the figures (a) and (b) are illustrative of operation in the region at or near the "0 mode while the figures (c) and (d) illustrate operation in the region at or near the 1r mode. The FIGS. 1:: and show top views of a stack of metallic disks comprising a conventional slow wave structure, while FIGS. 2a and show top views of a stack of metallic disks of which a slow wave structure made according to this invention is composed. FIGS. 1b and 1d show the magnetic field and the current flow directions for a conventional slow wave structure while FIGS. 2b and 2d show the same for the slow wave structure of this invention.

Referring now to FIGS. la-ld, there is shown schematically a conventional slow wave structure comprising a stack of metallic disks each provided with two coupling slots. In these figures, the numeral 1 denotes the metallic peripheral wall of a cylindrical waveguide and the numeral 2 denotes one of a plurality of circular metallic disks disposed perpendicular to the axis of the cylindrical wall 1, the various disks being spaced at equal intervals. A central hole 3 for passage of an electron beam is provided at the center of the disk 2 and two coupling slots 4 and 5 are also provided in the disk 2 in symmetrical relationship with respect to the axis or center of the hole 3.

FIG. 1b illustrates a longitudinal cross-section of the structure along the x-x' plane of FIG. la, which passes through the centers of the coupling slots 4 and 5. From this figure, it will be seen that a number of circular metallic disks 2, 2", and 2", each with the same physical configuration as the disk 2, are disposed periodically in the direction 2-2 of the axis of the cylindrical wall 1 to constitute a plurality of partitions in the slow wave structure. In the illustration, only four partitions are shown for simplicity, however, many more disks or partitions are of course provided in an actual slow wave structure.

FIGS. 1a and 1b illustrate the disk loaded waveguide slow wave structure operating in or near the 0 mode, the current flow and the magnetic field directions being indicated in FIG. 1b. Referring further to FIG. lb, it is 3,369,63il Patented Mar. 14, 1967 known that the currents on the opposite surfaces of each disk flow along the inner surface of the peripheral wall 1 in the same direction with respect to the axis z-z. The arrows 6, 6', and 6" in FIG. lb indicate the directions of these currents and the graphical symbols and (D indicate the magnetic field direction. As also illustrated in FIG. 1b, the currents flowing on the opposite surfaces of each disk or partition are opposite in direction to one another at each of the coupling slots 4 and 5, whereas the magnetic fields on the opposite sides of each partition are of the same polarity or sense at each of the coupling slots. Therefore, if the magnetic fields on the opposite sides of each partition are coupled at any coupling slot, there will be no possibility of the two magnetic fields cancelling one another out. Consequently, an electromagnetic wave is present extremely close to the inner peripheral wall surface and this structure exhibits resonance almost in the same manner as a large cavity having a radius R as seen in FIG. la. It may be said that the surface current flows radially Within the hatched sector area shown in FIG. 1a, avoiding the sectors in which the coupling slots 4 and 5 are provided.

By constrast, the potentials on the disks or partitions 2, 2, and 2 in the vicinity of the 7r mode region shown in FIGS. 1c and 1d become alternately of opposite polarity to each other. Accordingly, as illustrated in FIG. 1d, the currents 6, 6, 6 on the opposite surfaces of each disk or partition flow in the same direction or sense near the corresponding coupling slots 4-5, 45, and 4"5". For example, the directions of the currents 6 and 6' on the opposite surfaces of the partition 2' near the coupling slot 4 are the same. Consequently, the magnetic fields on the opposite sides of each partition become reversed in direction to each other, with the result that the resultant magnetic field intensity at or near either coupling slot becomes either nil or is markedly decreased. In other Words, the greater part of the electromagnetic wave exists in the cylindrical part inside the coupling slots and hence, the slow wave structure in the 1r mode resonance behaves as if it were a small cavity 7 having a radius r as shown by the dished line circle in FIG. 10. The small cavity -7, however, structurally involves no electrical conducting members for interconnecting these partitions near the periphery of the cavity. Therefore, this cavity manifests a high impedance value and a low Q value. In this case, mode stability of the slow wave structure is lessened and there is a tendency for unwanted modes to be induced in addition to the 1r mode, rendering it difficult to widen the frequency bandwidth and to increase the mutual action of electrons.

This invention eliminates these disadvantages inherent in conventional slow wave structures, FIG. 2 being a schematic illustration of one embodiment of the invention. In this figure, the numerals 1 through 7 indicate similar elements as in FIG. 1. FIGS. 2a and 2b illustrate schematically the operational behavior of this embodiment in or near the 0 mode while FIGS. 2c and 2d illustrate that in or near the 1r mode.

In accordance with the principles of this invention, a double cavity slow wave structure is formed with the partitions 2, 2, 2", and 2" interconnected by electrical shorting conductors 8 and 9 of suitable physical configuration at the inside of the opposed coupling slots 4 and 5 in a manner, for example, as shown in FIGS. 2a2d. In such structure, the electrical conductors or connecting bodies 8 and 9 pass through the partitions in peripheral regions adjacent the coupling slots 4 and 5, and most of the current, in flowing along the upper or lower surface of each disk, bypasses the sector regions (FIG. 2a), in which the coupling slots 4 and 5 are contained in much the same way as in a conventional structure operating in or near the 0 mode. In other words, the current distribution is materially unaffected by the presence of these shorting conductors 8 and 9.

In the vicinity of the 1r mode region, however, the shorting conductors 8 and 9 function in a manner as if they were a part of the peripheral wall of the small cavity 7 shown in FIG. 20, i.e., they form current return paths. Therefore, the magnetic field cancelling action due to the coupling slots 4 and 5 can be promoted in a more stable manner and the structure can operate as a cavity having a radius r as seen in FIG. 20 resulting in a higher Q value than a similar structure without the shorting conductors. Consequently, the band-pass of such a structure is substantially wider than that of a conventional structure while the Q value of such a small cavity with shorting conductors is high and therefore the mutual impedance of the electrons is increased. Among the features or advantages of this invention, therefore, are availability of an extremely wide pass bandwidth, an increase in the mutual impedance of electrons, and improvements in transmission efiiciency.

FIG. 3 illustrates schematically another embodiment of the invention. In the structure shown in this figure, three coupling slots 4, 5, and 10 are provided in each disk in symmetrical relationship with respect to the center of the disk. With this disk configuration, it may be said that a third coupling slot 10 and a third connecting body 11 in the form of a shorting conductor, have been added to the structure shown in FIG. 20. Further, adjacent ones of the coupling slots 4, 5, and 10 are connected with thin slits 12, 13, and 14 to enhance the function of the coupling slots.

Since the slits are arranged concentrically with the coupling slots of this construction, the coupling coetficient of the magnetic field components on the opposite sides of each coupling slot is increased and hence, the magnetic field cancelling action is enhanced. Consequently, a sufiiciently low operating frequency can be selected between the and 11- modes so that the mutual action of electrons is further improved.

Besides the important features or advantages referred to above, this invention has still other advantages. For example, the possibility of the production of unwanted modes is much less than with conventional slow wave structures because of the comparatively simple construction. Also, the structure may be used as an integral circuit element of a high power tube by circulating cooling air or water through the inside of the conducting members 8 and 9.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. An electron discharge device comprising a double cavity slow wave structure in the form of a stack of metallic disk partitions of similar physical configuration,

means for supporting said partitions at the peripheries thereof,

each of said partitions having a plurality of coupling slots,

and a plurality of electrical conducting bodies interconmeeting said partitions,

the points of interconnection being adjacent said coupling slots, whereby the improved characteristics of 4 higher Q, wider band-pass and higher impedance over conventional structures is achieved.

2. An electron discharge device for use in the microwave frequency region, said device having a double cavity slow wave structure comprising an outer supporting member,

a plurality of conductive partitions mounted generally within said supporting member,

said partitions being disposed generally parallel to one another and spaced from one another,

each of said partitions having a plurality of coupling slots therein,

and a plurality of electrically conductive members interconnecting said partitions,

15 the points of interconnection being adjacent said coupling slots and inwardly thereof toward the centers of said partitions, whereby the improved characteristics of higher Q, wider band-pass and higher impedance over conventional structures is achieved.

3. The invention described in claim 2, wherein said partitions each comprise a disk having a central aperture therein,

and coupling slots in adjacent disks are generally in alignment with one another.

4. The invention described in claim 2, wherein said outer supporting member comprises a cylindrical waveguide.

5. The invention described in claim 3, wherein said disks each include slits located between adjacent coupling SlOtS.

6. An electron discharge device for use in the microwave frequency region, said device having a double cavity slow wave structure comprising a cylindrical waveguide,

a plurality of metallic disk-shaped partitions mounted on said waveguide,

said partitions being disposed generally parallel to one another in spaced relationship,

a central aperture in each of said partitions,

40 a plurality of coupling slots in each of said partitions,

the slots in each partition being located in generally symmetrical relationship with respect to the center of its respective partition,

the slots in adjacent partitions being generally in alignment with one another along a path generally parallel to the central axis of said cylindrical waveguide,

and a shorting conductor adjacent eachv of said coupling slots in said partitions and interconnecting said partitions,

the points of interconnection being inward of said coupling slots toward said central apertures, whereby the improved characteristics of higher Q, wider bandpass and higher impedance over conventional structures is achieved.

7. The invention described in claim 6, wherein said coupling slots are generally of arcuate shape.

FOREIGN PATENTS 8/1963 Canada.

HERMAN KARL SAALBACH, Primary Examiner.

L. ALLAHUT, Assistant Examiner. 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING A DOUBLE CAVITY SLOW WAVE STRUCTURE IN THE FORM OF A STACK OF METALLIC DISK PARTITIONS OF SIMILAR PHYSICAL CONFIGURATION, MEANS FOR SUPPORTING SAID PARTITIONS AT THE PERIPHERIES THEREOF, EACH OF SAID PARTITIONS HAVING A PLURALITY OF COUPLING SLOTS, AND A PLURALITY OF ELECTRICAL CONDUCTING BODIES INTERCONNECTING SAID PARTITIONS, THE POINTS OF INTERCONNECTION BEING ADJACENT SAID COUPLING SLOTS, WHEREBY THE IMPROVED CHARACTERISTICS OF HIGHER Q, WIDER BAND-PASS AND HINGER IMPEDANCE OVER CONVENTIONAL STRUCTURES IN ACHIEVED. 